scholarly journals Mantle-derived arc related mafic enclaves and host orthogneiss from the Shyok Suture Zone of NE Ladakh, India: An evidence of magma-mixing

2013 ◽  
Vol 47 (1) ◽  
pp. 1-19
Author(s):  
D. RAMESHWAR RAO ◽  
MEGHA M. DAGA ◽  
HAKIM RAI
Keyword(s):  
Magma Mixing ◽  
Suture Zone ◽  
Mafic Enclaves

scholarly journals Magma Mixing Genesis of the Mafic Enclaves in the Qingshanbao Complex of Longshou Mountain, China: Evidence from Petrology, Geochemistry, and Zircon Chronology

Minerals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 195 ◽  
Author(s):  
Wenheng Liu ◽  
Xiaodong Liu ◽  
Jiayong Pan ◽  
Kaixing Wang ◽  
Gang Wang ◽  
...  
Keyword(s):  
Host Rock ◽  
Inductively Coupled Plasma ◽  
Magma Mixing ◽  
Coarse Grained ◽  
Calc Alkaline ◽  
Quartz Crystals ◽  
Alkaline Rocks ◽  
Mafic Enclaves ◽  
Normal Zoning ◽  
Host Rocks

The Qingshanbao complex, part of the uranium metallogenic belt of the Longshou-Qilian mountains, is located in the center of the Longshou Mountain next to the Jiling complex that hosts a number of U deposits. However, little research has been conducted in this area. In order to investigate the origin and formation of mafic enclaves observed in the Qingshanbao body and the implications for magmatic-tectonic dynamics, we systematically studied the mineralogy, petrography, and geochemistry of these enclaves. Our results showed that the enclaves contain plagioclase enwrapped by early dark minerals. These enclaves also showed round quartz crystals and acicular apatite in association with the plagioclase. Electron probe analyses showed that the plagioclase in the host rocks (such as K-feldspar granite, adamellite, granodiorite, etc.) show normal zoning, while the plagioclase in the mafic enclaves has a discontinuous rim composition and shows instances of reverse zoning. Major elemental geochemistry revealed that the mafic enclaves belong to the calc-alkaline rocks that are rich in titanium, iron, aluminum, and depleted in silica, while the host rocks are calc-alkaline to alkaline rocks with enrichment in silica. On Harker diagrams, SiO2 contents are negatively correlated with all major oxides but K2O. Both the mafic enclaves and host rock are rich in large ion lithophile elements such as Rb and K, as well as elements such as La, Nd, and Sm, and relatively poor in high field strength elements such as Nb, Ta, P, Ti, and U. Element ratios of Nb/La, Rb/Sr, and Nb/Ta indicate that the mafic enclaves were formed by the mixing of mafic and felsic magma. In terms of rare earth elements, both the mafic enclaves and the host rock show right-inclined trends with similar weak to medium degrees of negative Eu anomaly and with no obvious Ce anomaly. Zircon LA-ICP-MS (Laser ablation inductively coupled plasma mass spectrometry) U-Pb concordant ages of the mafic enclaves and host rock were determined to be 431.8 5.2 Ma (MSWD (mean standard weighted deviation)= 1.5, n = 14) and 432.8 4.2 Ma (MSWD = 1.7, n = 16), respectively, consistent with that for the zircon U-Pb ages of the granite and medium-coarse grained K-feldspar granites of the Qingshanbao complex. The estimated ages coincide with the timing of the late Caledonian collision of the Alashan Block. This comprehensive analysis allowed us to conclude that the mafic enclaves in the Qingshanbao complex were formed by the mixing of crust-mantle magma with mantle-derived magma due to underplating, which caused partial melting of the ancient basement crust during the collisional orogenesis between the Alashan Block and Qilian rock mass in the early Silurian Period.

scholarly journals Heat- and melt-fluxed melting of lower continental crust: Insights from two types of subduction-related granitoids in northeastern China and the implications for crustal reworking and growth

Lithosphere ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 488-506
Author(s):  
Xing-Hua Ma ◽  
Shi-Lei Qiao ◽  
Peng Xiang ◽  
Andrei V. Grebennikov ◽  
Renjie Zhou
Keyword(s):  
Continental Crust ◽  
Continental Margin ◽  
Lower Crust ◽  
Magma Mixing ◽  
Hybrid Origin ◽  
Plate Boundaries ◽  
Mafic Enclaves ◽  
Primary Location ◽  
Crustal Reworking ◽  
Zircon Saturation

AbstractConvergent plate boundaries are the primary location for the formation of continental crust by the intrusion of arc batholiths that contain essentially mantle-derived magmas. This paper presents two types of arc granitoids (enclave-free monzogranites and enclave-bearing granodiorites) in northeastern (NE) China to understand crustal evolution and growth in the eastern Asian continental margin. The monzogranites (189 Ma) show characteristics typical of upper continental crust, with high SiO2 contents and enrichment of K, Rb, and Pb. These monzogranites have low ISr (87Sr/86Sr) ratios (0.70378–0.70413) and positive εNd (t) (+2.2 to +2.3) and εHf (t) (+7.3 to +10.2) values. These features, combined with high zircon saturation temperatures (TZr > 800 °C), suggest that the monzogranites were generated by the heat-fluxed melting of juvenile lower crust. In contrast, the granodiorites (171 Ma) contain abundant coeval mafic enclaves and show relatively low silica contents, low TZr (748–799 °C), and particularly wide variation in εHf (t) (−3.5 to +5.6), implying a hybrid origin involving both mantle- and crust-derived components. Isotopic modeling indicates that mantle material accounts for around 60%–70% of the hybrid magmas by volume. The granodiorites have adakite-like signatures (e.g., Sr/Y > 21 and [La/Yb]N > 15), which may have been primarily caused by a process of magma mixing and hornblende-dominated fractional fractionation, rather than through melting of a subducting slab or thickened lower crust. The two distinct granitoids (monzogranites and granodiorites) represent continental crustal reworking and growth, respectively, related to the subduction of the Paleo-Pacific Plate beneath the eastern Asian continental margin during the Jurassic.

scholarly journals Bimodal magmatism as a consequence of the post-collisional readjustment of the thickened Variscan continental lithosphere (Aiguilles Rouges-Mont Blanc Massifs, Western Alps)

2000 ◽  
Vol 91 (1-2) ◽  
pp. 221-233 ◽  
Author(s):  
François Bussy ◽  
Jean Hernandez ◽  
Jürgen Von Raumer
Keyword(s):  
Magma Mixing ◽  
Western Alps ◽  
Continental Lithosphere ◽  
Mafic Enclaves ◽  
Mantle Sources ◽  
Major Scale ◽  
Isothermal Decompression ◽  
Back Arc ◽  
Transcurrent Faults ◽  
Tectonic Exhumation

High Precision U-Pb zircon and monazite dating in the Aiguilles Rouges–Mont Blanc area allowed discrimination of three short-lived bimodal magmatic pulses: the early 332 Ma Mg–K Pormenaz monzonite and associated 331 Ma peraluminous Montées Pélissier monzogranite; the 307 Ma cordierite-bearing peraluminous Vallorcine and Fully intrusions; and the 303 Fe-K Mont Blanc syenogranite. All intruded syntectonically along major-scale transcurrent faults at a time when the substratum was experiencing tectonic exhumation, active erosion recorded in detrital basins and isothermal decompression melting dated at 327-320 Ma. Mantle activity and magma mixing are evidenced in all plutons by coeval mafic enclaves, stocks and synplutonic dykes. Both crustal and mantle sources evolve through time, pointing to an increasingly warm continental crust and juvenile asthenospheric mantle sources. This overall tectono-magmatic evolution is interpreted in a scenario of post-collisional restoration to normal size of a thickened continental lithosphere. The latter re-equilibrates through delamination and/or erosion of its mantle root and tectonic exhumation/erosion in an overall extensional regime. Extension is related to either gravitational collapse or back-arc extension of a distant subduction zone.

Tracing magma mixing and crystal–melt segregation in the genesis of syenite with mafic enclaves: Evidence from in situ zircon Hf–O and apatite Sr–Nd isotopes

Lithos ◽  
2019 ◽  
Vol 334-335 ◽  
pp. 42-57 ◽  
Author(s):  
Jin-Feng Sun ◽  
Ji-Heng Zhang ◽  
Jin-Hui Yang ◽  
Yue-Heng Yang ◽  
Shi Chen
Keyword(s):  
Magma Mixing ◽  
Nd Isotopes ◽  
Mafic Enclaves ◽  
Melt Segregation

scholarly journals Identifying the ingredients of hydrous arc magmas: insights from Mt Lamington, Papua New Guinea

2019 ◽  
Vol 377 (2139) ◽  
pp. 20180018 ◽  
Author(s):  
M. C. S. Humphreys ◽  
J. Zhang ◽  
G. F. Cooper ◽  
C. G. Macpherson ◽  
C. J. Ottley
Keyword(s):  
Papua New Guinea ◽  
Subduction Zones ◽  
Magma Mixing ◽  
New Guinea ◽  
Surface Expression ◽  
Magma Intrusion ◽  
Mafic Enclaves ◽  
Reservoir Architecture ◽  
Element Partitioning ◽  
Plumbing Systems

Volcanism is the surface expression of magma intrusion, crystallization, assimilation and hybridization processes operating throughout the crust over a range of time periods. Many magmas, including those erupted at subduction zones, have complex textures that reflect these processes. Here, we use textural and geochemical characteristics of calcic amphiboles to help identify multiple ingredients of subduction zone magmatism at Mt Lamington volcano, Papua New Guinea. Our approach uses existing trace element partitioning schemes to calculate the compositions of amphibole equilibrium melts (AEMs). The AEM compositions show that Mt Lamington andesites and plutonic enclaves are dominated by fractionation of amphibole + plagioclase + biotite, with assimilation of plagioclase and zircon. Magnesiohastingsite crystals in the andesite and diktytaxitic mafic enclaves reflect multiple episodes of recharge by more primitive, geochemically variable melts. The andesite also contains clots with rounded grains and melt on grain boundaries. These features indicate slow crystallization, and the retention of melt films could significantly enhance the potential for remobilization of crystals by infiltrating melts or during magma mixing. Variations in crystallization conditions could thus significantly affect the mush microstructure. We suggest that this could result in a significant bias of the volcanic record towards the preferential incorporation of more slowly cooled plutonic material from the lower crust or from more thermally mature plumbing systems. This article is part of the Theo Murphy meeting issue ‘Magma reservoir architecture and dynamics’.

The Minastira peraluminous granite, Puno, southeastern Peru: a quenched, hypabyssal intrusion recording magma commingling and mixing

1997 ◽  
Vol 61 (409) ◽  
pp. 743-764 ◽  
Author(s):  
Daniel J. Kontak ◽  
Alan H. Clark
Keyword(s):  
Large Range ◽  
Magma Mixing ◽  
Chemical Diffusion ◽  
Peraluminous Granite ◽  
Mafic Enclaves ◽  
Fine Grained ◽  
Physico Chemical ◽  
Chemical Conditions ◽  
End Members ◽  
Spike Patterns

AbstractThe Minastira granite, a c. 25 Ma subvolcanic plug of fine-grained granitic rock in the Cordillera Oriental of SE Peru, has preserved textures indicative of a history involving mixing of at least two magmas, a volumetrically dominant felsic component and a less voluminous mafic one. The felsic component is represented by variably fractured, altered and embayed crystals of quartz, feldspar, biotite with minor coarsegrained melt- and fluid-inclusion rich apatite, and possible cordierite (now a pseudomorphous Fe-Mg phase), whereas the mafic component is represented by calcic plagioclase. The process of magma mixing is reflected by: (1) ubiquitous sieved-textured plagioclase with complex textural relationships; (2) a large range in plagioclase compositions with reversals and spike patterns in profiles; (3) embayed and internally fractured (thermal shock?) quartz; (4) the rare occurrence of pyroxene coronas on quartz; and (5) textures within biotite suggestive of its incipient breakdown. The lack of mafic enclaves indicates that physico-chemical conditions of the mixing were conducive to homogenization (i.e. chemical diffusion) and a superficially homogeneous rock is now observed. The association of glomeroclasts of crystals originating from both the mafic and felsic end members and a quenched quartz-feldspar matrix indicate that the mixing occurred in an underlying magma chamber.

scholarly journals Chemical Evolution of Calc-alkaline Magmas during the Ascent through Continental Crust: Constraints from Methana, Aegean Arc

2020 ◽  
Vol 61 (3) ◽  
Author(s):  
Milena V Schoenhofen ◽  
Karsten M Haase ◽  
Christoph Beier ◽  
Dominic Woelki ◽  
Marcel Regelous
Keyword(s):  
Trace Element ◽  
Continental Crust ◽  
Fractional Crystallization ◽  
Magma Mixing ◽  
Basaltic Magma ◽  
High Water ◽  
Calc Alkaline ◽  
Mafic Enclaves ◽  
Aegean Arc ◽  
Mineral Compositions

Abstract Quaternary calc-alkaline andesitic to dacitic lavas effusively erupted on top of about 30 km thick accreted continental crust at Methana peninsula in the western Aegean arc. We present new data of major and trace element concentrations as well as of Sr–Nd–Pb isotope ratios along with mineral compositions of Methana lavas and their mafic enclaves. The enclaves imply a parental basaltic magma and fractional crystallization processes with relatively little crustal assimilation in the deep part of the Methana magma system. The composition of amphibole in some mafic enclaves and lavas indicates deeper crystallization at ∼25 km depth close to the Moho compared with the evolved lavas that formed at <15 km depth. The presence of amphibole and low Ca contents in olivine suggest high water contents of ∼4 wt% in the primitive magmas at Methana. The compositions of andesitic and dacitic lavas reflect fractional crystallization, assimilation of sedimentary material, and magma mixing in the upper 15 km of the crust. The Methana magmas have fO2 of FMQ + 1 to FMQ + 2 (where FMQ is the fayalite–magnetite–quartz buffer) at temperatures of 1200 to 750 °C and the fO2 does not vary systematically from mafic to felsic compositions, suggesting that the mantle wedge was oxidized by sediment subduction. Amphibole is an important fractionating phase in the more evolved Methana magmas and causes significant changes in incompatible element ratios. Although xenocrysts and mineral compositions indicate magma mixing, the major and trace element variation implies only limited mixing between dacitic and basaltic melts.

Evidence for mixed contribution of mantle and lower and upper crust to the genesis of Jurassic I-type granites from Macao, SE China

2020 ◽  
Vol 133 (1-2) ◽  
pp. 37-56 ◽  
Author(s):  
Pedro Quelhas ◽  
João Mata ◽  
Ágata Alveirinho Dias
Keyword(s):  
Magma Mixing ◽  
Mineral Chemistry ◽  
Granitic Rocks ◽  
Geochemical Data ◽  
Mafic Enclaves ◽  
Group I ◽  
High K ◽  
Depleted Mantle ◽  
Charge And Radius ◽  
Se China

Abstract Much controversy has occurred in the past few decades regarding the nature of the sources, the petrogenetic processes, and the tectonic regime(s) of the Jurassic magmatism within the Southeast China magmatic belt. This study aims to contribute to the discussion with mineral chemistry, and whole-rock element and Sr-Nd-Hf-Pb isotopic geochemical data from granitic rocks and microgranular mafic enclaves from Macao, where two discrete groups of I-type biotite granites have been identified (referred to as Macao Group I [MGI] and Macao Group II [MGII]). It is proposed that the granitic magmas were generated by partial melting of infracrustal medium- to high-K, basaltic Paleoproterozoic to Mesoproterozoic protoliths (Nd depleted mantle model age [TDM2] = 1.7–1.6 Ga and Hf TDM2 = 1.8–1.6 Ga), triggered by underplating of hot mantle-derived magmas in an extensional setting related to the foundering of a previously flat slab (paleo–Pacific plate) beneath the SE China continent. The main differences between the two groups of Macao granites are attributed to assimilation and fractional crystallization processes, during which upper-crustal Paleozoic metasediments were variably assimilated by MGI magmas. This is evidenced by an increase in initial 87Sr/86Sr ratios with degree of evolution, presence of metasedimentary enclaves, and high percentage of zircon xenocrysts with Paleozoic ages. In addition, other processes like late-stage fluid/melt interaction and magma mixing also left some imprints on granite compositions (rare earth element tetrad effect plus non–charge-and-radius-controlled behavior of trace elements and decoupling between different isotope systems, respectively). The distribution of isotopically distinct granites in SE China reflects the nature of the two Cathaysia crustal blocks juxtaposed along the Zhenghe-Dapu fault.

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